Some of the Donegal eagles have been collected from eyries that have been laden with live prey. Sometimes these carcasses might be crawling with maggots because the eagles have caught more food than they can eat. But the Irish birds are collected from the most successful pairs of Scottish eagles, as we are only allowed collect donor stock from nests with two young (i.e. the best and most productive 5-10% of the population). Many nests in Scotland fail due to a shortage of food during and even before the breeding season, as females fail to reach the required body condition for a long breeding season. Bad weather can be detrimental as prey may be less active and hunting can be suspended during heavy driving rain. Golden Eagles have a very long breeding season (approx 4 months), including a longer incubation period than any other Irish bird (except possibly Mute Swans), and a very long fledging period. Breeding performance is often closely related to food availability.
Prey remains in the Glenveagh nest and its immediate vicinity in 2007 showed at least 10 Irish Hares were taken, 2 badger cubs and a fox cub and two Red Grouse. Golden Eagles hunt live prey and also eat carrion, especially during the winter. Golden Eagles utilise a wide variety of prey across their breeding range in the Northern and Southern Hemisphere, especially medium sized birds (Grouse, Crows, Ravens, Seagulls, duck) and mammals (Hares, rabbits, Fox and badger cubs) (Watson 1997 and Brown 1976). But they can occasionally take frogs, other birds of prey and even hunt snakes and catch and drop turtles onto rocks in the Mediterranean. Depending on the abundance and availability of food, eagle pairs tend to be either specialist or generalist hunters. The most successful pairs seem to concentrate on just a few prey species, whereas others pairs are generalists only if their preferred prey items are somewhat scarce.
Golden Eagles in Ireland eat dead Sheep, dead Deer, Hares and Rabbits, foxes and badgers, crows and Ravens, grouse –which is quite similar to the Scottish diet. We have little data on the eagles that have visited some of Ireland’s coastal areas but presume rabbits and seabirds are important for these birds. However within the Scottish regions there are marked variations between the eagles in terms of which prey or carrion items are favoured. Where Hares and/or Grouse were plentiful, eagles tended to have a smaller dietary breadth (range of species caught). Most of its live prey will range in weight from 500g to 2kgs.